The first aspect of the present invention relates generally to a thermal transfer sheet and a multicolor thermal transfer recording method, and more particularly to a thermal transfer sheet that enables plain paper printing and multicolor recording when printing is carried out with thermal color-developing paper, a multicolor thermal transfer method, and a multicolor printed matter.
The second aspect of the present invention relates generally to an edged or rimmed image and a method of forming the same, and more specifically to an image that is formed with a hue different from that of the background in which the image is formed and is rimmed with white or other color and a method of forming the same.
So far, color output has been achieved by thermal color development, thermal transfer, ink-jet, electrophotography or other techniques. Among these, the ink-jet technique has recently enjoyed an increasing use for the reason that it can output color images more easily than would be possible with other techniques. With this technique, it is possible to output colors for paper of size A4 or so within a relatively short time. However, much time is now needed to output colors for paper of larger size, esp., size A1 or banners, and costly equipment is required as well. In addition, the obtained image has a problem in terms of water resistance and so is unsuitable for outdoor purposes. Electrophotography has some merits in that output time is short and an image of good-enough durability is obtainable although the principle of toner fixation takes part in this. However, this technique is not readily available because equipment is expensive to buy and maintain.
On the other hand, the thermal color-developing recording technique using thermal color-developing paper and a thermal head is shorter in terms of output time than other techniques. In addition, the cost of equipment used for large color output is not much higher than that of equipment used with other techniques. The thermal transfer technique using a thermal transfer sheet and a thermal head, because of using a pigment type of coloring material, has the advantage of being capable of forming a color image excellent in durability such as light fastness, and accordingly can be used outdoors. This technique can output a color image at relatively low cost.
For the thermal transfer printing technique, a thermal transfer sheet has been used, which includes a thermally transferable ink layer (hereinafter called simply an ink layer) formed on one surface of a substrate film. This conventional thermal transfer sheet is prepared by coating an ink layer comprising a mixture of wax with a pigment, dye or other coloring agent on a substrate film such as paper of 10 .mu.m to 25 .mu.m in thickness, for instance, condenser or paraffin paper, or a plastic film of 2 .mu.m to 25 .mu.m in thickness, for instance, a polyester or cellophane film.
In general, the thermal color-developing technique has wide application, because it can output descriptions or patterns at much lower cost as compared with the thermal transfer technique; in other words, the unit cost of printing becomes low as output size becomes large. In addition, several approaches have been proposed to multicolor printing used in combination with this thermal color-developing technique.
The thermal color-developing method is particularly excellent in expressing a single color, but various means are needed for recording a multicolor image, e.g., a two- or three-image.
As disclosed in JP-B 49-69 as an example, there has been proposed a multicolor printing method in which an applied energy is varied by use of a multilayer structure comprising color-developing layers having varying melting points. With this method, however, it is not always easy to form a bright color because the layer having a higher melting point develops an unclear color.
One means for making multicolor recording using thermal color-developing paper is to provide a double- or triple-layer structure for color development on the thermal color-developing paper. For instance, JP-A 57-178791 discloses the provision of two color-developing layers that differ in color-developing temperature and coloration, between which there is an intermediate layer containing a decoloring agent that makes the color developed by one of the color-developing layers invisible. By varying the printing temperature it is thus possible to make printing in two different colors.
On the other hand, a method of using thermal color-developing paper as the so-called cooperative member wherein an ink layer is transferred from a thermal transfer sheet to the color-developing surface thereof while the hue of the ink layer of the thermal transfer sheet is differently combined with the hue of the color developed by the thermal color-developing paper, thereby making it easy to form an image of two or more colors, is proposed in JP-B 3-25355 and JP-B 3-32476. Another method comprising a combination of transfer technique with color-developing paper such as one mentioned above has been proposed as well (JP-A 59-42996 and JP-A 56-157395), but this has a similar problem as mentioned above. In addition, JP-A 63-315292 discloses use of thermally color-developed paper. Only the required portion of the paper is then made invisible by use of a decoloring agent present in a thermal transfer sheet for the so-called white printing. This method is used as a presentation tool for OHP and other purposes.
In the case of the thermal paper disclosed in JP-A 57-178791 that is designed to develop two colors, however, some limitation is placed on the combination of the colors to be printed, once the colors to be developed have been determined. In other words, although there is no problem in terms of two-color recording, practical difficulty is involved in four-, five- or more-color recording. In the case of the method disclosed in JP-B 3-32476 wherein two-color recording is achieved by the combination of low-temperature transfer with high-temperature color development, on the other hand, it is impossible to achieve multicolor recording in bright, e.g., blue or red, colors, because at high temperature the image is inevitably recorded in a mixture of the color of the ink layer with the color developed by the color-developing paper. In the case of the method disclosed in JP-B 3-25355 wherein two-color recording is achieved by the combination of low-temperature color development with high-temperature transfer to the contrary, color mixing during high-temperature transfer unavoidably occurs, as mentioned just above. Moreover, the method disclosed in JP-A 63-315292 is to prepare the so-called white characters or logos and so lends itself to OHP image formation, but cannot form any multicolor image.
One possible approach to solving such problems is to incorporate white or other pigment of high hiding power in the ink layer or in the outer subordinate layer thereof (see JP-A 2-214694). However, this makes the color tone of the ink layer light or pastel; so making clear color printing impossible. Moreover, some considerable printing energy is needed because the hiding layer deprives heat of a thermal head.
Therefore, the first object of the present invention is to provide a thermal transfer sheet that enables plain paper to be printed with thermal energy used so far in the art and clear and versatile multicolor recording to be made even on thermal color-developing paper, a multicolor recording method, and a printed matter.
Heretofore, so-called edged or rimmed images have been available for various images inclusive of characters or logos, or for ad-posters, and illustrated books for infants and juveniles of the lower classes. One typical rimmed image is shown in FIG. 6 wherein a white area 62 that is similar in shape to, and somewhat larger in size than, a desired image is formed in a colored background 61 on thermal color-developing paper 60, and an image 63 that is similar in shape to, and somewhat smaller than, the area 62 is formed therein by printing.
The above rimmed image is usually formed as by offset printing, gravure printing, and screen printing. No cost-effectiveness problem arises in mass-printing, although at least two plates are needed and printing operation is troublesome. However, these printing techniques incur some considerable expense when making a small amount of prints such as ad-posters and propaganda leaflets distributed as by stores, and discount tags; that is, they must manually be made. However, it is very difficult to manually make dozens of the same image.
Therefore, the second object of the present invention is to provide a means for making aesthetically excellent rimmed images in a very simple way.